The European Commission proposed on Wednesday a new law allowing individual EU countries to restrict or prohibit imported genetically modified crops even if they have been approved by the bloc as a whole.

The proposal covering GM crops in human food and animal feed upset trading partners, notably the United States, which wants Europe to open its doors fully to U.S. GM crops as part of a planned EU-U.S. free trade deal.

U.S. Trade Representative Michael Froman expressed his disappointment, saying it appeared to divide the European Union into 28 separate markets for certain products.

"Proposing this kind of trade-restrictive action is not constructive." he said in a statement.

The proposal has also drawn criticism from environmental groups, who fear the new rules do not provide the legal grounds for national governments to opt out, opening them up to legal challenges from biotech companies or the United States.

The Commission said member states that opted out would have to justify their decision to do so without referring to health or environmental issues already assessed at EU level.

The new law would mirror legislation signed last month by the European parliament covering the cultivation of GM crops in the European Union, giving member states a similar opt-out right.

Widely grown in the Americas and Asia, GM crops have divided opinion in Europe. Britain is broadly in favor of them, while France is among the countries that opposes them.

Only one GM crop is currently grown in Europe: Monsanto's maize MON810 in Spain and Portugal.

However, there are 58 GM crops approved for use in feed and food in the European Union, the Commission said.

In practice, there are hardly any GM products on sale for human consumption, but some 60 percent of the EU's needs of vegetable proteins for cattle are met by imported soy and soymeal from countries where GM cultivation is widespread.

The biotech industry and the United States have repeatedly complained that while there is a clear process for approving GM products in Europe, it appears to be blocked.

Industry group EuropaBio says the Commission has not cleared any crops since November 2013. There are 59 crops pending approval, with 17 awaiting a final decision from the Commission after clearing checks by the European Food Safety Authority.

Additional reporting by Barbara Lewis and Krista Hughes in Washington.